The recording density of a magnetic disk has been increased recently and the recording density of the current hard disk drive (HDD) is in the order of several hundreds giga-bits. With such increased recording density of the magnetic disk, a floating distance of a magnetic head from a magnetic disk is reduced.
A recent magnetic head assembly includes a suspension spring in the order of 15 mm×20 mm and a slider of several to 1 mm square provided in a top portion of the suspension spring, in which a gap between a thin film magnetic head and a magnetic disk is reduced to in the order of several to 10 nm.
The performance test of a magnetic disk as an information recording medium of HDD and a magnetic head (magnetic head assembly) for reading and writing data with respect to the magnetic disk are precisely performed by a tester in the manufacturing step.
HDD of 3.5 inches to 1.8 inches and smaller than 1.0 inch are used in automobile parts, home electric products and audio products. Therefore, reduction of cost and mass production of HDD are requested. Under such requests, a magnetic head tester which can efficiently test a large amount of magnetic disks and miniaturization of the magnetic disk tester are requested.
In order to improve the test efficiency of the magnetic disk or the magnetic head, JP-A-2001-52319 and JP-A-2006-179107 describe a tester having a plurality of test decks and processing signals from the magnetic heads by distributing signals from the test decks between the test decks or selectively switching the test decks.
The test deck of the conventional magnetic head tester includes 1 or 2 spindles for one carriage and it is usual that one measuring portion is assigned to each spindle. And, a new magnetic head assembly is tested after a test of a magnetic head assembly is ended. This switching is performed by hand work.
The test is interrupted during the switching of magnetic head and the measuring portion which receives a read signal from the magnetic head becomes standby state. Therefore, the test efficiency of the magnetic head assembly is dropped. On the other hand, the size of magnetic head assembly is reduced and a mounting and demounting of a magnetic head assembly with respect to a head clamp table of a head carriage which are necessary for the magnetic head test and are performed by using a mounting hole having a protruded edge portion. Therefore, through-put of the head test depends on the switching work of the magnetic head assembly.
In order to improve the efficiency of the magnetic head test, JP-A-2001-52319 describes a technique in which a pair of magnetic head assemblies are arranged on both sides of a magnetic disk opposing each other and tested alternately. In such case, it is necessary to exchange one of the magnetic heads during a test of the other magnetic head. The size and configuration of the current magnetic head assembly is very small as mentioned previously and, when a magnetic head floats from a magnetic disk by a small gap of several to 10 nm, even when one of the magnetic heads is exchanged by the other magnetic head by moving the one magnetic head from the magnetic disk to a vicinity of its periphery during the test of the other magnetic head, the exchange must be performed carefully and so a noise problem occurs in the electrical measurement of the magnetic head under the test.
JP-A-2006-179107 discloses a method in which, in order to improve through-put, two spindles are used alternately. However, the use of one of two magnetic heads is not always completed during a test of the other magnetic head and cross-talk noise may occur in the simultaneous tests of the magnetic heads.
Further, when a tested magnetic head assembly on the spindle is completed is exchanged by a magnetic head assembly to be tested manually, the improvement of the through-put of the testing is limited.
It may be necessary to automate the exchange operation of magnetic head assemblies. In order to load a magnetic head assembly by deriving the magnetic head assembly from a tray (or pallet) and automatically position it on a head clamp table of a head carriage and, after a test is ended, unload it automatically by using a handling robot, high positioning accuracy of the handling robot is required.
Further, since the head clamp table and a clamp mechanism of magnetic head assembly on the head clamp table are provided on a movable table of the head carriage, moving mass and speed in head access and head loading/unloading speeds of them become important. Therefore, it is very difficult practically to freely design and change them. As a result, it is preferable to realize the automation of the exchange operation of magnetic head assembly by performing transfer of magnetic head assembly between the handling robot and the head clamp table and clamping operation on the basis of the clamp operation based on a spring or a mechanism therefore.